Beltless high velocity air blower

ABSTRACT

A direct drive, high velocity, high power centrifugal air blower. The blower employs a high-speed electric motor (&gt;15,000 rpm) having an output drive shaft that is directly coupled to an impeller rotatably housed within a volute. The assembly enables the impeller to rotate at speeds up to 100,000 rpm without the need for either step-up gears or belts and pulleys interposed between the motor output drive shaft and the impeller. The elimination of an indirect coupling assembly between the motor ouput shaft and the impeller provides a high power, high velocity blower/vacuum with greater reliability than indirectly coupled assemblies.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a centrigugal air blower and,more particularly, to a high-speed (˜100,000 rpm) air blower employing ahigh-speed electric motor directly coupled to an impeller.

[0003] 2. Prior Art

[0004] A centrifugal fan in accordance with the current art includes amotor and a motor-driven impeller comprising a plurality of fan bladesarranged at a predetermined pitch around a rotation axis. By rotatingthe plurality of the blades on the rotation axis, air is taken in thedirection of the rotation axis and discharged in a direction that isboth tangential to the rotation of the plurality of the blades andorthogonal to the rotation axis. A volute (housing) is disposed aroundthe impeller and directs the flow of air through the fan. In order tomove a large volume of air through the fan in a relatively short periodof time, it is desirable to operate the impeller at a high rotationalrate (˜20,000 rpm or higher). Since higher power (greater than aboutthree kilowatts ) electric motors normally operate at a maximum of 3600rpm, a “V” belt and pulley assembly or gearing is employed between themotor output shaft and the impeller in order to rotate the impeller at ahigher velocity than the motor's rotational velocity.

[0005] Examples of centrifugal fans in accordance with the prior art aredisclosed U.S. Pat. Nos. 6,210,118; 5,964,576; 5,813,834; 5,707,209;5,478,201; 5,474,422; 5,324,167; 5,165,857; 5,156,524; 5,141,397;4,913,621; 4,874,293; 4,662,830; 4,531,890; 4,265,592 and 4,061,441.These representative disclosures of prior art centrifugal fans, whilenot exhaustive, teach a centrifugal fan comprising either a low-speeddirect coupled motor-impeller assembly or a high-speed indirectlycoupled motor-impeller assembly.

[0006] Noise is a common problem with centrifugal fans. One source ofnoise is the impeller. Miyazawa, in U.S. Pat. No. 6,488,472, discloses alow-noise axial fan having an impeller comprising a plurality of bladesarranged around a rotation axis at predetermined and varied layoutpitches. For instance, the layout pitch between the two adjacent bladesmay be different from the layout pitch between the remaining blades.Miyazawa asserts that the arrangement of blades controls the whirringsound of the fan, which whirring sound is increased when the blades arearranged at an equal layout pitch.

[0007] Fujita, et al., in U.S. Pat. No. 5,964,576 disclose an impellerfor a centrifugal fan having fifty or more blades of not larger than 250mm in outer diameter which has a casing and a multi-blade impellerrotatably supported in the casing. A centrifugal force is applied to airentering an inlet formed on the casing when the impeller is rotated, andhigh pressure air is ejected through an outlet formed on a portion ofthe casing. An outer peripheral surface of the impeller is inclined orcurved so as to have an inlet side large diameter portion and a bladeholding base side small diameter portion, or is stepped so as to have aninlet side cylindrical outer peripheral surface of large diameter and ablade holding base side cylindrical outer peripheral surface of smalldiameter connected to the inlet side cylindrical outer peripheralsurface. The inlet side cylindrical outer peripheral surface and theblade holding base side cylindrical outer peripheral surface aresubstantially the same height

[0008] A drive belt and pulley assembly interposed between the outputdrive shaft of the motor and the impeller, which is in accordance withthe prior art fan assemblies operating at rotational velocities above15,000 rpm, is yet another source of both mechanical failure and noise.In addition, at high rotational velocities, the impeller must beperfectly balanced in order to maintain its structural integrity andproduce a low level of noise. There remains a need for a centrifugal fanthat can operate at rotational velocities between 15,000 and 100,000 rpmat a relatively low level of noise with minimal mechanical failure.

SUMMARY

[0009] It is an object of the present invention to provide adirect-drive centrifugal fan operable at rotational velocities between15,000 and 100,000 rpm.

[0010] It is a further object of the invention to provide a centrifugalfan meeting the above objective and further comprising an efficient,low-noise impeller.

[0011] The features of the invention believed to be novel are set forthwith particularity in the appended claims. However the invention itself,both as to organization and method of operation, together with furtherobjects and advantages thereof may be best understood by reference tothe following description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a longitudinal cross-sectional view of a centrifugal fanassembly in accordance with the present invention.

[0013]FIG. 2 is a perspective view of an impeller for a centrifugal fanin accordance with the present invention.

[0014]FIG. 3 is a transverse cross-sectional view of the impeller ofFIG. 2 taken along section line 3-3.

[0015]FIG. 4 is an end view (viewed from the right in FIG. 1) of theimpeller illustrated in FIGS. 2 and 3, rotatably housed within a volute.The motor is not visible in the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Prior art high-speed centrifugal fans employ mechanicalamplification to cause an impeller to rotate at speeds greater than therotational speed of the motor which, in accordance with the prior art,operates at 3600 rpm. The term “high-speed motor”, as used herein,refers to an electric motor operating at speeds greater than 3600 rpmand, most preferably, at speeds greater than 15,000 rpm. Theinterposition of mechanical amplification means such as pulleys and adrive belt or gears disposed between the motor output shaft and theimpeller in order to increase the rotational velocity of the impellerintroduces a source of potential failure into the assembly.

[0017]FIG. 1 is a longitudinal cross-sectional view of a direct-drivehigh-speed centrifugal fan assembly, indicated at numeral 10, inaccordance with the present invention. The centrifugal fan 10 includes ahigh-speed motor 11 having an axial output shaft 12, a distal end 12 aof shaft 12 being directly attached to an impeller 13. A volute 14having an air output port 15 substantially encloses the impeller 13. Inoperation, air is drawn into an air intake port 16 of the volute 14 bythe rotating blades of the impeller 13 and forced through the air outputport 15 to generate a high-velocity working air stream adjacent theoutput port 15 which may be used, for example, for ventilating moistureor a volatile solvent from a work area. The term “ventilating” meansthat the centrifugal fan may be employed either as a blower or as avacuum.

[0018] An impeller suitable for efficient operation at high velocitiesis illustrated in perspective view in FIG. 2 and in transversecross-section in FIG. 3. The impeller 13 comprises a circular plate 20supporting: (a) a cylindrical post 21 having an axially disposed bore 21a dimensioned to receive the motor drive shaft 12 a (FIG. 1)therewithin; and (b) a plurality of blades 22 mounted on an outersurface thereof. Each of the blades 22 has a curvilinear outer edge 23and a curvilinear inner edge 24 abutting the outer surface of thecylindrical post 21 and affixed thereto. Each blade 22 further has astraight top edge 25 and a curvilinear bottom edge 26 affixed to thecircular plate 20. The four edges 23, 24, 25 and 26 bound an arcuatelycontoured blade surface 27.

[0019] While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. For example, thecentrifugal fan in accordance with the present invention may be employedeither as a blower or as a vacuum. It is therefore intended to cover inthe appended claims all such changes and modifications that are withinthe scope of this invention.

What we claim is:
 1. A centrifugal fan consisting essentially of: (a) anelectric motor operable for rotating a drive shaft at rotationalvelocities greater than 15,000 rotations per minute; (b) an impelleraffixed to said drive shaft; and (c) a volute substantially enclosingsaid impeller, said volute having an axially disposed air intake portand a tangentially disposed air output port.
 2. The centrifugal fan ofclaim 1 wherein said impeller comprises a plurality of bladessymmetrically mounted on a circular plate and radiating outwardly froman axially disposed rotation axis, each of said blades having anarcuately contoured blade surface, the plurality of the blades beingoperable for receiving air in a direction of the rotation axis throughsaid air intake port and for discharging the air tangentially throughsaid air outlet port in said volute.